The invention relates to a waveguide-type optical control device and a process for producing the same, and more particularly to a waveguide-type optical control device, which has a directional coupler-type Mach-Zehnder construction and can improve the ratio of the minimum attenuation level to the maximum attenuation level (extinction ratio) without complicating the construction, and a process for producing the same.
Waveguide-type optical control devices are suitable for integration and a reduction in power consumption, and, thus, studies have been made on the utilization of waveguide-type optical control devices in optical switches or optical modulators. Further, in recent years, the spread of dense wavelength division multiplexing (DWDM) has lead to an increasing demand for variable optical attenuators as means for making optical powers of respective wavelengths uniform at the time of wavelength multiplexing, or as optical parts of optical ADMs (add drop multiplexers) which select a desired wavelength and inserts/removes the wavelength in a transmission line. Among others, variable optical attenuators having a directional coupler-type Mach-Zehnder (MZ) construction comprising two directional couplers provided on an LiNbO3 (lithium niobate; LN) substrate, which is advantageous from the viewpoints of a reduction in size, a reduction in voltage, and a reduction in power consumption, and a phase shifter provided between the two directional couplers are being put to practical use.
FIG. 1 shows the construction of a conventional waveguide-type optical control device having a directional coupler-type Mach-Zehnder construction. In FIG. 1, a variable optical attenuator is exemplified as the waveguide-type optical control device.
The variable optical attenuator having a directional coupler-type Mach-Zehnder construction comprises: optical waveguides 1a, 1b which are provided parallel to each other on an LN substrate (not shown); a first directional coupler 2 provided within the optical waveguides 1a, 1b; a phase shifter 3 provided adjacent to the first directional coupler 2; and a second directional coupler 4 provided adjacent to the phase shifter 3. The phase shifter 3 comprises a first electrode 3a, a second electrode 3b, and a third electrode 3c. The third electrode 3c is used as a common electrode. A negative (xe2x88x92) voltage is applied to this electrode from a direct current power supply 3d, and a positive (+) voltage is applied to the first electrode 3a and the second electrode 3b from the direct current power supply 3d to cause an electric field.
Next, the operation of the waveguide-type optical control device (variable optical attenuator) shown in FIG. 1 will be explained. A signal light introduced from the end of the optical waveguide 1a is branched in the first directional coupler 2 into signal light parts which are to be traveled respectively through optical waveguides 1a and 1b (branching ratio=50:50), and the branched signal lights are then input into the phase shifter 3. The phase shifter 3 operates according to the magnitude of an applied voltage 31 from the direct current power supply 3d. When the voltage 31 is not applied from the direct current power supply 3d, the branched signal lights introduced into the optical waveguides 1a and 1b are input in an identical phase into the second directional coupler 4 and the whole light is output from the output terminal of the optical waveguide 1b while no light is output from the optical waveguide 1a. 
Next, when the applied voltage 31 is increased from 0 (zero) volt, the refractive index of the optical waveguides 1a and 1b are changed and, consequently, the propagation speed of signal lights, which travel respectively through the optical waveguides 1a and 1b, is changed. Since the voltage applied to the optical waveguide 1a is opposite in direction to the voltage applied to the optical waveguide 1b, a difference occurs in propagation speed between signal light, which travels through the optical waveguide 1a, and signal light which travels through the optical waveguide 1b in the phase shifter 3. As a result, the signal light in the optical waveguide 1a and the signal light in the optical waveguide 1b are input in a mutually different phase into the second directional coupler 4. For this reason, the branching ratio (coupling rate) of the second directional coupler 4 is deviated from the original rate 50%, and, as a result, a part of signal light, which, up to this stage, has been entirely output from the optical waveguide 1b in the second directional coupler 4, is also output from the optical waveguide 1a. When the applied voltage 31 is increased to about 30 to 50 V, the signal light is substantially entirely output from the optical waveguide 1a. That is, setting the applied voltage 31 to a suitable value permits the coupling length L in the phase shifter 3 to be equivalently changed and, consequently, permits optical output corresponding to the change to be obtained.
When the voltage 31 was not applied, or when a voltage of about 30 to 50 V was applied, in order to output the whole signal light from any one of the optical waveguide 1a and the optical waveguide 1b in the second directional coupler 4, the branching ratio (coupling rate) of the first directional coupler 2 to the second directional coupler 4 should be accurately brought to 50:50 (50%). To this end, the length of a portion where the optical waveguides 1a and 1b approach each other (coupling length L=xcfx80/2xcex3 wherein xcex3 represents Pockels constant) should be accurately brought to the half of the complete coupling length Lc (=xcfx80/2xcexa wherein xcexa represents coupling coefficient). The deviation of the branching ratio (coupling rate) of the first directional coupler 2 to the second directional coupler 4 from 50:50 (50%) results in increased leakage of the light signal from one waveguide to the other waveguide at the output terminal of the second directional coupler 4 and thus deteriorates the ratio of the minimum attenuation level to the maximum attenuation level (extinction ratio).
FIG. 2 shows the relationship between the gap and the coupling length in a directional coupler.
The length of a portion, where the optical waveguides la and 1b approaches and are coupled to each other (coupling length L), and a gap G are important to the directional coupler. In order to bring the branching ratio (coupling rate) to 50:50 (50%), it is necessary to eliminate a variation in the gap G and to bring the coupling length L to [complete coupling length Lc÷2]. These two are important parameters for a production process of the directional coupler.
FIG. 3 shows that characteristics vary according to the production parameters. When there is no variation in gap G shown in FIG. 2 and, at the same time, when the coupling length L is equal to the half of the complete coupling length Lc, ideal characteristics 130 are obtained, that is, the crosstalk is minimized and, consequently, the extinction ratio is increased. On the other hand, when there is a variation in gap G or when the coupling length L is not equal to the half of the complete coupling length Lc, deteriorated characteristics 131 are obtained. It is known that a change in coupling rate only by several percents from 50% causes this state.
In order to solve this problem, Japanese Patent Publication No. 72964/1994 proposes a construction such that, separately from electrodes for the phase shifter, electrodes for directional couplers are provided in the directional couplers in the optical waveguides to control the refractive index in the optical waveguides, thereby equivalently regulating the coupling length L. This construction will be explained in conjunction with FIG. 4.
FIG. 4 shows another conventional waveguide-type optical control device. Also in FIG. 4, a variable optical attenuator is used as the waveguide-type optical control device.
A first directional coupler 2, a phase shifter 3, and a second directional coupler 4 are disposed in series between the input terminal and the output terminal of the optical waveguides 1a and 1b. For applying a bias voltage, electrodes 20a, 20b are provided in the first directional coupler 2, electrodes 30a, 30b are provided in the phase shifter 3, and electrodes 40a, 40b are provided in the second directional coupler 4. The refractive index in the first and second directional couplers 2, 4 are controlled by properly setting the voltage applied to the electrodes 20a, 20b and the electrodes 40a, 40b. As a result, the coupling length L is equivalently regulated, and a deterioration in extinction ratio is improved.
Further, Japanese Patent Laid-Open No. 142569/1998 proposes a directional coupler having a construction which can reduce the level of leakage between optical waveguides and can improve dynamic range. Specifically, this publication proposes a construction which brings the coupling length L in the directional coupler to a double length of the complete coupling length Lc or a length obtained by multiplying the complete coupling length Lc by an even number.
The conventional waveguide-type optical control devices, however, have the following problems. In the construction proposed in Japanese Patent Publication No. 72964/1994 wherein dedicated electrodes are independently provided for the phase shifter and the two directional couplers, the device size of the variable optical attenuator is disadvantageously increased. Further, since the electrodes are disposed in three blocks, the number of sites where voltage control should be performed is increased. This disadvantageously complicates the construction of the control circuit.
On the other hand, according to the construction proposed in Japanese Patent Laid-Open No. 142569/1998, the coupling length L is at least twice of the complete coupling length Lc. That is, the total length of the device is long, and, thus, it is impossible to reduce the size of the device.
Accordingly, it is an object of the invention to provide a waveguide-type optical control device, which can improve the extinction ratio and the dynamic range without the complication of the construction and can realize a reduction in size, and a process for producing the waveguide-type optical control device.
According to the first feature of the invention, a waveguide-type optical control device comprises:
first and second directional couplers provided while leaving a predetermined spacing therebetween, said first and second directional couplers being constituted respectively by two right and left optical waveguides provided on a substrate; and
a phase shifter provided between the first directional coupler and the second directional coupler, first, second, and third electrodes being provided respectively on the left side of the left optical waveguide, on the right side of the right optical waveguide, and between the two optical waveguides, said phase shifter functioning to control light, which passes through the two optical waveguides, according to a voltage applied to the first, second, and third electrodes,
said first, second, and third electrodes being extended into the first and second directional couplers.
According to this construction, the first, second, and third electrodes are extended from the phase shifter into the first and second directional couplers, and, thus, the voltage applied to the phase shifter as such is also applied to the first and second directional couplers to control the refractive index of the first and second directional couplers. By virtue of this, since the coupling length is equivalently regulated, a deterioration in extinction ratio can be suppressed. Further, since the number of electrodes in the directional coupler is identical to that in the phase shifter, there is no need to increase the size of the device, and, in addition, the complication of the control system can be avoided.
According to the second feature of the invention, a waveguide-type optical control device comprises:
a phase shifter provided with a first electrode section comprising an electrode provided on the left side of a left optical waveguide, an electrode provided on the right side of a right optical waveguide, and an electrode provided between the two optical waveguides; and
a directional coupler comprising two optical waveguides which are connected respectively to the two right and left optical waveguides in the phase shifter and are provided parallel to each other with the spacing between the two optical waveguides being partially reduced, said directional coupler being used in at least one of an optical branching section provided on the input side of the phase shifter and an optical coupling section provided on the output side of the phase shifter, the refractive index of the two optical waveguides being varied according to a voltage applied across the electrodes provided respectively on the left side of the left optical waveguide and the right side of the right optical waveguide and the electrode provided between the two optical waveguides in the phase shifter,
said directional coupler being provided with a second electrode section comprising an electrode provided on the left side of the left optical waveguide, an electrode provided on the right side of the right optical waveguide, and an electrode provided between the two optical waveguides, the three electrodes constituting the second electrode section being electrically connected respectively to the three electrodes constituting the first electrode section provided adjacent to the second electrode section in the longitudinal direction of the two optical waveguides, the voltage applied to the first electrode section being applied to the second electrode section.
According to this construction, the directional coupler used in the optical branching section or the optical coupling section comprises, in its coupling portion, a second electrode section having three electrodes, i.e., a first electrode provided on the left side of the left optical waveguide, a second electrode provided on the right side of the right optical waveguide, and a third electrode provided between the two optical waveguides, and the electrodes in this second electrode section are separately and electrically connected respectively to three electrodes of the first electrode section in the phase shifter, whereby the voltage applied to the first electrode section in the phase shifter is simultaneously applied to the electrodes of the second electrode section in the directional coupler. By virtue of this construction, the refractive index in the directional coupler is controlled by the voltage applied to the phase shifter. As a result, the coupling length L is equivalently regulated to suppress the deterioration in extinction ratio. Further, since insulation between the electrodes in the phase shifter and the electrodes in the directional coupler is not required, there is no need to provide a space between these electrodes. This can eliminate the need to increase the size of the waveguide-type optical control device, and, in addition, the complication of the control system can be avoided.
According to the third feature of the invention, a waveguide-type optical control device comprises:
a phase shifter comprising two left and right optical waveguides, a first electrode provided on the left side of the left optical waveguide, a second electrode provided on the right side of the right optical waveguide, and a third electrode provided between the two optical waveguides;
a first directional coupler that is connected to one end of the phase shifter and functions to branch an optical signal introduced through one of the two optical waveguides into optical signal parts which are then introduced respectively into the two optical waveguides; and
a second directional coupler that is connected to the other end of the phase shifter and functions to couple the optical signal parts received respectively from the two optical waveguides,
at least one of the first and second electrodes and the third electrode having been extended into a part or the whole of the first directional coupler or the second directional coupler.
According to this construction, the first, second, and third electrodes in the phase shifter are extended into a part or the whole of the first directional coupler or the second directional coupler using common optical waveguides. Therefore, upon the application of the voltage across the electrodes in the phase shifter, an electric field is applied to the phase shifter and, at that same time, is also applied to the first or second directional coupler, whereby the refractive index in the directional coupler is also controlled. As a result, since the coupling length L is equivalently regulated, the deterioration in extinction ratio can be suppressed. Further, since insulation between the electrodes in the phase shifter and the electrodes in the directional coupler is not required, there is no need to provide a space between these electrodes. This can eliminate the need to increase the size of the waveguide-type optical control device, and, in addition, the complication of the control system can be avoided.
According to the fourth feature of the invention, a waveguide-type optical control device comprising:
a phase shifter comprising two left and right optical waveguides, a first electrode provided on the left side of the left optical waveguide, a second electrode provided on the right side of the right optical waveguide, and a third electrode provided between the two optical waveguides;
a first directional coupler that is connected to one end of the phase shifter and functions to branch an optical signal introduced through one of the two optical waveguides into optical signal parts which are then introduced respectively into the two optical waveguides; and
a second directional coupler that is connected to the other end of the phase shifter and functions to couple the optical signal parts received respectively from the two optical waveguides,
at least one of the first and second electrodes and the third electrode having been extended into a part or the whole of the first directional coupler, at least one of the first and second electrodes and the third electrode having been extended into a part or the whole of the second directional coupler.
According to this construction, in addition to the third feature of the invention, the first, second, and third electrodes in the phase shifter are extended into a part or the whole of both the first directional coupler and the second directional coupler. Therefore, upon the application of the voltage to the electrodes in the phase shifter, an electric field is applied to the phase shifter and, at the same time, is also applied to the first and second directional couplers from the electrode portion provided in the first and second directional couplers, whereby the refractive index in each of the directional couplers is controlled. As a result, since the coupling length L is equivalently regulated, the deterioration in extinction ratio can be suppressed. Further, since insulation between the electrodes in the phase shifter and the electrodes in the directional coupler is not required, there is no need to provide a space between these electrodes. This can eliminate the need to increase the size of the waveguide-type optical control device, and, in addition, the complication of the control system can be avoided.
According to the fifth feature of the invention, a waveguide-type optical control device comprising:
a phase shifter comprising two left and right optical waveguides, a first electrode provided on the left side of the left optical waveguide, a second electrode provided on the right side of the right optical waveguide, and a third electrode provided between the two optical waveguides;
a first directional coupler that is connected to one end of the phase shifter and functions to branch an optical signal introduced through one of the two optical waveguides into optical signal parts which are then introduced respectively into the two optical waveguides; and
a second directional coupler that is connected to the other end of the phase shifter and functions to couple the optical signal parts received respectively from the two optical waveguides,
said first directional coupler comprising, in its directional coupling section, first directional coupling section outer electrodes disposed respectively at a portion near the left side of the left optical waveguide and at a portion near the right side of the right optical waveguide in the first directional coupling section and a first directional coupling section intermediate electrode disposed between the two optical waveguides in the first directional coupling section,
said first electrode and said second electrode having been electrically connected respectively to the first directional coupling section outer electrodes, said third electrode having been electrically connected to the first directional coupling section intermediate electrode.
According to this construction, the first directional coupler using optical waveguides common to the first directional coupler and the phase shifter comprises first directional coupling section outer electrodes disposed respectively at a portion near the left side of the left optical waveguide and at a portion near the right side of the right optical waveguide in the first directional coupling section and a first directional coupling section intermediate electrode disposed between the two optical waveguides in the first directional coupling section, and the first, second, and third electrodes in the phase shifter are electrically connected respectively thereto. Therefore, upon the application of the voltage across the electrodes in the phase shifter, an electric field is applied to the phase shifter and, at the same time, is also applied to the first directional coupler, whereby the refractive index in the directional coupler is controlled. As a result, since the coupling length L is equivalently regulated, the deterioration in extinction ratio can be suppressed. Further, since insulation between the electrodes in the phase shifter and the electrodes in the directional coupler is not required, there is no need to provide a space between these electrodes. This can eliminate the need to increase the size of the waveguide-type optical control device, and, in addition, the complication of the control system can be avoided.
According to the sixth feature of the invention, a waveguide-type optical control device comprises:
a phase shifter comprising two left and right optical waveguides, a first electrode provided on the left side of the left optical waveguide, a second electrode provided on the right side of the right optical waveguide, and a third electrode provided between the two optical waveguides;
a first directional coupler that is connected to one end of the phase shifter and functions to branch an optical signal introduced through one of the two optical waveguides into optical signal parts which are then introduced respectively into the two optical waveguides; and
a second directional coupler that is connected to the other end of the phase shifter and functions to couple the optical signal parts received respectively from the two optical waveguides,
said second directional coupler comprising, in its directional coupling section, second directional coupling section outer electrodes disposed respectively at a portion near the left side of the left optical waveguide and at a portion near the right side of the right optical waveguide in the second directional coupling section and a second directional coupling section intermediate electrode disposed between the two optical waveguides in the second directional coupling section,
said first electrode and said second electrode having been electrically connected respectively to the second directional coupling section outer electrodes, said third electrode having been electrically connected to the second directional coupling section intermediate electrode.
According to this construction, the second directional coupler using optical waveguides common to the second directional coupler and the phase shifter comprises second directional coupling section outer electrodes disposed respectively at a portion near the left side of the left optical waveguide and at a portion near the right side of the right optical waveguide in the second directional coupling section and a second directional coupling section intermediate electrode disposed between the two optical waveguides in the second directional coupling section, and the first, second, and third electrodes in the phase shifter are electrically connected respectively thereto. Therefore, upon the application of the voltage across the electrodes in the phase shifter, an electric field is applied to the phase shifter and, at the same time, is also applied to the second directional coupler, whereby the refractive index in the directional coupler is controlled. As a result, since the coupling length L is equivalently regulated, the deterioration in extinction ratio can be suppressed. Further, since insulation between the electrodes in the phase shifter and the electrodes in the directional coupler is not required, there is no need to provide a space between these electrodes. This can eliminate the need to increase the size of the waveguide-type optical control device, and, in addition, the complication of the control system can be avoided.
According to the seventh feature of the invention, a variable optical attenuator comprises:
a phase shifter provided with a first electrode section comprising an electrode provided on the left side of a left optical waveguide, an electrode provided on the right side of a right optical waveguide, and an electrode provided between the two optical waveguides; and
a directional coupler comprising two optical waveguides which are connected respectively to the two optical waveguides in the phase shifter and are provided parallel to each other with the spacing between the two optical waveguides being partially reduced, said directional coupler being used in at least one of an optical branching section provided on the input side of the phase shifter and an optical coupling section provided on the output side of the phase shifter, the refractive index of the two optical waveguides being varied according to a voltage applied across the electrodes provided respectively on the left side of the left optical waveguide and the right side of the right optical waveguide and the electrode provided between the two optical waveguides in the phase shifter, whereby the attenuation level of the lights passed through the optical waveguides is controlled,
said directional coupler being provided with a second electrode section comprising an electrode provided on the left side of the left optical waveguide, an electrode provided on the right side of the right optical waveguide, and an electrode provided between the two optical waveguides, the three electrodes constituting the second electrode section being electrically connected respectively to the three electrodes constituting the first electrode section provided adjacent to the second electrode section in the longitudinal direction of the two optical waveguides, the voltage applied to the first electrode section being applied to the second electrode section.
According to this construction, the directional coupler used in the optical branching section or the optical coupling section comprises, in its region, a second electrode section having three electrodes, i.e., a first electrode provided on the left side of the left optical waveguide, a second electrode provided on the right side of the right optical waveguide, and a third electrode provided between the two optical waveguides, and the electrodes in this second electrode section are separately and electrically connected respectively to three electrodes in the first electrode section in the phase shifter, whereby the voltage applied to the first electrode section in the phase shifter is simultaneously applied to the electrodes of the second electrode section in the directional coupler. By virtue of this construction, the refractive index in the directional coupler is controlled by the voltage applied to the phase shifter to control the attenuation level of the optical signals which pass through the optical waveguides. Further, since insulation between the electrodes in the phase shifter and the electrodes in the directional coupler is not required, there is no need to provide a space between these electrodes. This can eliminate the need to increase the size of the variable optical attenuator, and, in addition, the complication of the control system (attenuation level control circuit) can be avoided.
According to the eighth feature of the invention, an optical equalizer comprises:
an optical demultiplexer into which a wavelength multiplexed optical signal containing a plurality of optical signals with one or mutually different wavelengths is input and which demultiplexes the wavelength multiplexed optical signal into optical signals and outputs the demultiplexed optical signals;
the variable optical attenuator according to the seventh feature of the invention which selectively attenuates the demultiplexed optical signals by a predetermined attenuation level and outputs the attenuated optical signals; and
an optical multiplexer for multiplexing the attenuated optical signals output from the variable optical attenuator.
According to this construction, the optical equalizer comprises an optical demultiplexer for demultiplexing the input wavelength multiplexed optical signal, a variable optical attenuator for attenuating, to a predetermined level, the optical signals output from the optical demultiplexer, and an optical multiplexer for multiplexing optical signals from each variable optical attenuator. As described above in connection with the seventh feature of the invention, in the variable optical attenuator, the electrodes provided in the phase shifter separately and electrically connected to adjacent electrodes in the directional coupler. Therefore, upon the application of the voltage to the phase shifter, an electric field can be also applied to the directional coupler to control the attenuation level of the optical signals which pass through the optical waveguides. This can realize matching of optical signal levels. Thus, since insulation between the electrodes in the phase shifter and the electrodes in the directional coupler is not required, there is no need to provide a space between these electrodes. Further, since a common applied voltage can be used, the size of the variable optical attenuator can be reduced, and the necessity of increasing the size of the optical equalizer can be avoided.
According to the ninth feature of the invention, an optical inserting/separating apparatus comprises:
an optical demultiplexer into which a wavelength multiplexed optical signal containing a plurality of optical signals with one or mutually different wavelengths is input and which demultiplexes the wavelength multiplexed optical signal into optical signals and outputs the demultiplexed optical signals;
a wavelength varying filter for selectively separating an optical signal with a predetermined wavelength from the demultiplexed optical signals;
the variable optical attenuator according to the seventh feature of the invention which selectively attenuates the demultiplexed optical signals, which have passed through the wavelength varying filter, by a predetermined attenuation level and outputs the attenuated optical signals; and
a filter which selects and outputs the attenuated optical signals from the variable optical attenuator or externally inserted optical signals; and
an optical multiplexer for multiplexing the attenuated optical signals output from the filter or the inserted optical signals.
According to this construction, optical signals with predetermined wavelengths are selectively separated from the optical signals, which have been demultiplexed by the optical demultiplexer, through a wavelength varying filter, and the level of the optical signals, which have been passed through the filter, is then attenuated to a desired level by the variable optical attenuator. The optical signals from the variable optical attenuator or externally inserted optical signals are selected by a filter and output. The optical signals from individual filters are multiplexed in the optical multiplexer, and are output as the wavelength multiplexed optical signal. In the variable optical attenuator, the first electrode section in the phase shifter is electrically connected to the second electrode section in the directional coupler. Therefore, a common applied voltage can be used for the application of a voltage across the electrodes. This can minimize the space necessary for the arrangement of the electrodes and can simplify the control system, whereby the size of the variable optical attenuator can be reduced and, in its turn, the size of the optical equalizer can be reduced.
According to the tenth feature of the invention, a waveguide-type optical control device comprises:
a phase shifter comprising two left and right optical waveguides, a first electrode provided on the left side of the left optical waveguide, a second electrode provided on the right side of the right optical waveguide, and a third electrode provided between the two optical waveguides;
a first directional coupler that is connected to one end of the phase shifter and functions to branch an optical signal introduced through one of the two optical waveguides into optical signal parts which are then introduced respectively into the two optical waveguides; and
a second directional coupler that is connected to the other end of the phase shifter and functions to couple the optical signal parts received respectively from the two optical waveguides,
at least one of the first and second electrodes and the third electrode having been extended into a part or the whole of the first directional coupler or the second directional coupler, the third electrode in its extended electrode portion being provided so that a longitudinal electric field is applied to one of the two optical waveguides.
According to this construction, the first, second, and third electrodes in the phase shifter are extended into a part or the whole of the first directional coupler or the second directional coupler using common optical waveguides, and, at the same time, the extended portion of the third electrode in the directional coupler is provided so that a longitudinal electric field is applied to one of the optical waveguides. Therefore, upon the application of the voltage across the electrodes in the phase shifter, an electric field is applied to the phase shifter and, at the same time, is also applied from the vertical direction (thicknesswise direction of the electrodes) to the first or second directional coupler to control the refractive index. Since the longitudinal electric field can be applied, in the case of an identical voltage, a strong electric field can be applied while, in the case of an identical electric field, the applied voltage can be lowered. Further, since the coupling length L is equivalently regulated, a deterioration in extinction ratio can be reduced. Further, since insulation between the electrodes in the phase shifter and the electrodes in the directional coupler is not required, there is no need to provide a space between these electrodes. This can eliminate the need to increase the size of the waveguide-type optical control device, and, in addition, the complication of the control system can be avoided.
According to the eleventh feature of the invention, a process for producing a waveguide-type optical control device, comprises the steps of:
forming two right and left optical waveguides so as to construct a phase shifter and at least one directional coupler within a substrate;
forming a first electrode and a second electrode respectively on the left side of the left optical waveguide and on the right side of the right optical waveguide so as to extend from the phase shifter to a part of the directional coupler, forming a third electrode between the two optical waveguides so as to extend from the phase shifter to a part of the directional coupler, and, in addition, forming a plurality of independent electrode pieces at a predetermined interval at the end of the second electrode and at the end of the third electrode, or forming a plurality of electrode pieces at a predetermined interval connected to each other or one another in a cascade form through a fuse; and
successively wire bonding the necessary number of the plurality of independent electrode pieces from the inner side, or successively fusion cutting the fuse of the necessary number of the plurality of cascaded electrode pieces from the outer side so as to bring the characteristic value of the directional coupler to a desired value.
According to this production process, after a phase shifter and at least one directional coupler are formed by two optical waveguides, the first, second, and third electrodes are formed respectively in predetermined regions of the phase shifter and the directional coupler. In the directional coupler, a plurality of electrode pieces are connected in a cascade form to the end of the first electrode and the end of the second electrode through a fuse or a bonding wire. By virtue of this construction, the length of the first and second electrodes can be finely adjusted. That is, tuning can be performed to provide ideal characteristics.